Conventionally, for example as disclosed in Japanese Laid-Open Patent Application 8-284626, a solenoid valve for use as an intake or exhaust valve of an internal combustion engine is known. This solenoid valve is provided with an armature moving with an engine valve as a unity, a pair of solenoid coils disposed above and below the armature, and springs pushing the engine valve toward a neutral position.
When neither of the solenoid coils is supplied with an exciting current, the engine valve and the armature are held in the neutral position. Further, when an upper solenoid coil is supplied with the exciting current, the engine valve and the armature are attracted to the upper solenoid coil, while the engine valve and the armature are attracted to a lower solenoid coil when the lower solenoid coil is supplied with the exciting current. Therefore, according to the above described conventional solenoid valve, the engine valve can be operated so as to be opened and closed by alternately supplying the solenoid coils with proper exciting currents. In this case, ends of movement on closing and opening sides of the engine valve are controlled by the adhesion of the armature to the solenoid coils. Therefore, if electromagnetic forces generated by the solenoid coils can be made to promptly vanish in positions near the ends of movement of the engine valve, an excellent operational responsiveness of the solenoid valve can be realized, and the control of an impact sound and the improvement in durability are made possible because impact forces exerted between the armature and the solenoid coils are reduced.
For this purpose, the exciting currents supplied to the solenoid coils are controlled by a bridged-H-type circuit in the above described conventional solenoid valve. This bridged-H-type circuit includes a total of four switching means disposed respectively between terminals of the solenoid coil, and cathode and anode sides of a power supply. According to the bridged-H circuit, the solenoid coil can be energized in a predetermined direction by setting one pair of the switching means which are disposed diagonally across the solenoid coil to an ON state and the other pair to an OFF state. Further, the solenoid coil can be energized in the reverse direction by reversing the above described ON and OFF states. Therefore, the electromagnetic force generated by the solenoid coil can be made to promptly vanish by energizing the solenoid coil in the reverse direction to the exciting current by switching the ON and OFF states of the switching means of the bridged-H-type circuit when the engine valve approaches the end of movement.
However, as described above, the above described conventional solenoid valve requires four switching means for each of the solenoid coils. That is, eight switching means will be required for one solenoid valve as one solenoid valve is provided with two solenoid coils. Therefore, when the above described conventional solenoid valve is applied to an engine of a four-cylinder-four-valve type, for example, one hundred and twenty-eight switching means will be required, thus causing the cost of an actuating apparatus for actuating the solenoid valves to rise.